The Upper Cretaceous succession in northern South America is significant because the related rock deposits are among the most prolific oil sources in the region. Although several geological studies ...have focussed on this period, we still have poor knowledge of the exact deposition time of the lithostratigraphic units. In this study, we constructed a chronostratigraphic framework based on U–Pb ages and time-calibrated carbon isotopic events to constrain the chronostratigraphy of the Upper Cretaceous formations. The carbon isotope curve of the La Luna-1 core allowed us to identify several oceanic anoxic events also identified in the stratotypes of the Upper Cretaceous formations. The La Luna-1 also preserves a complete record of ash beds, from which zircons were extracted for U–Pb dating. The stratigraphic distribution of the ash beds indicates a crucial influence of volcanic activity during the Late Cretaceous. Sedimentological descriptions and mineralogical analysis were used to establish the primary lithological differences between the units. The Upper Cretaceous formations can be categorised as mixed rocks comprising variable percentages of carbonates, quartz and clay minerals. They also show silicification and, to a lesser extent, dolomitisation and recrystallisation. The Salada, Pujamana, and Galembo formations range in age between the Cenomanian and Coniacian, whereas the overlying La Renta Formation spans from the Santonian to at least the middle Campanian. The top of the La Renta Formation corresponds to a regional disconformity that contacted the middle Campanian with the Maastrichtian.
•The Cretaceous was characterized by high burial rates of carbon in the form of carbonates and organic carbon, much of the latter forming a significant proportion of the hydrocarbon source rocks in many sedimentary basins around the world, including South America.•The late Cretaceous of northern South America preserves a very complete record of the oceanic anoxic events (OAEs) that have been reported globally.•The late Cretaceous was characterized by the occurrence of an important volcanic activity.•The La Luna Formation was deposited between the Cenomanian and Santonian and their former members (Salada, Pujamana, and Galembo) should be elevated to the category of formations.
Reseña del libro de autoría del historiador peruano Pablo Luna, publicado en 2017, cuyo contenido compuesto por cinco capítulos con dos anexos de cuadros informativos que, en base a documentación ...original del Archivo arzobispal de Lima y del Convento de la Buenamuerte proporciona una visión completa y compleja de la constitución y declive de los religiosos camilos en Perú, centrada particularmente en la conformación del patrimonio que la convirtió en una “orden religiosa azucarera”.
Twelve landing ellipses (15 × 30 km each) were previously selected during the preliminary science and safety assessment of details of the Russian Luna-Glob mission. In our work, we have conducted a ...photogeological and topographical study of the top three most desirable landing ellipses (ellipses 1, 4, and 6) and modelled the thickness of the lunar basin ejecta at these locations in order to characterize their safety conditions and possible sources of materials. For all three potential landing sites large (>0.3–0.5 m) boulders do not represent a significant threat to the mission. The major safety concerns are small but abundant craters whose walls are steeper than the technical constraint of 7°. We have collected the data on density, areal fraction, and the mean distance between the neighboring steep-wall craters, which allow us to rank the safety of terrains within each landing ellipse. A set of morphologically and topographically distinctive units make up the surface of the landing ellipses. The units form two groups, the hilly units and the flat plains. The hilly units within the ellipses 1 and 6 are among the safest terrains. The flat plains of ellipses 1 and 4 represent the most unsafe surfaces. The ejecta of the South Pole-Aitken basin (SPA) strongly dominate the Luna-Glob landing zone and constitute ∼95% (by volume) of materials than can be encountered and analyzed within the landing ellipses. For example, the hilly units in the ellipses 1 and 6 likely represent materials of the SPA ejecta. In the ellipse 4, the hilly unit corresponds to the ejecta of Moretus crater and may represent materials excavated from below the SPA ejecta blanket. However, the small area and configuration of the hilly unit in ellipse 1 and abundant small steep-wall craters on the hilly unit in ellipse 4 make them either a difficult or an unsafe target to land. The flat plains in ellipses 1 and 4 are the most unsafe terrains to land because of the abundant steep-wall craters on their surfaces. Materials ejected by the large craters Boguslawsky and Boussingault from the lower portions of the SPA ejecta blanket make up the majority of the hilly unit in the landing ellipse 6. This unit is among the safest terrains in all top three landing ellipses of the Luna-Glob mission.
•The sources of materials in the top-three (1, 4, 6) Luna-Glob landing sites were analyzed.•The ejecta of the SPA basin dominate the entire Luna Glob landing area.•Flat plains in ellipses 1 and 4 may represent materials ejected from below the SPA ejecta.•Flat plains in ellipses 1 and 4 are the most unsafe units to land.•Units in ellipse 6 may represent materials from the lower portions of the SPA ejecta.
Epicontinental seas were important features of the paleogeographic landscape during the Cretaceous; however, the role they played as sinks of organic carbon is still poorly understood. The La Luna ...Formation (Albian-Coniacian) is a series of organic-rich limestones deposited in northwestern South America on an epicontinental sea (the La Luna Sea). This formation offers a forty-million-year continuous record of environmental change characterized by periods of oceanic anoxia in an epicontinental sea. The La Luna Sea, may have played an important role –although so far unexplored– in carbon cycling through the ocean during the Cretaceous, specifically during short-term, global-scale disruptions in the carbon cycle known as oceanic anoxic events (OAEs). To evaluate the role of the La Luna Sea in global carbon cycle perturbations, we conducted a detailed lithological and chemostratigraphic analysis of two stratigraphic sections from the Upper Magdalena Basin of Colombia, both of which encompass the Oceanic Anoxic Event 2 (OAE2) at the Cenomanian–Turonian boundary. Compared to deposits in the modern ocean, the La Luna Formation has high total organic carbon (TOC) before, during, and after OAE2. Foraminifera and nannoplankton assemblages also imply a stressed upper water column during OAE2. Geochemical and paleontological evidence suggests that the sediment-water interface was anoxic across the late Cenomanian and early Turonian. Strata deposited just after OAE2, however, contain inoceramid bivalves, consistent with short-lived re‑oxygenation of the benthic layer. Estimates of primary productivity, the covariation of Mo and U enrichment factors, and relations between Cd, Mo, Co, and Mn also reveal that the La Luna Sea was biogeochemically similar to the modern Cariaco Basin.
Despite high concentrations of organic carbon found in the La Luna Formation, mass-accumulation rates of organic carbon are low, a finding that can be explained by a reduction in the accumulation rate of sediments caused by the peak of sea-level transgression that took place at the Cenomanian–Turonian transition. Based on the areal extent of the La Luna Sea and mass-accumulation rates of organic carbon, 1.7 Eg of C were removed from the ocean over 500 ky and deposited in the La Luna Sea. Interestingly, although the La Luna Sea was one-third the size of the Western Interior Seaway (WIS), the amount of organic carbon buried in the WIS during OAE2 was similar (1.4 Eg of C). In these two epicontinental seas, 3.1 Eg of C were removed from the ocean during OAE2, accounting only for 3.4% of the total C needed to cause a perturbation of the carbon cycle similar to that observed during OAE2. The low amount of organic carbon buried in the La Luna Sea and the WIS suggests that neither of these inland seas were responsible for the efficient removal of organic carbon from the ocean during OAE2. This conclusion challenges the explanation that epicontinental seas were major sinks of organic carbon—and therefore they did not play a significant role in the carbon cycle during the Mesozoic OAEs and other disruptions of the carbon cycle in Earth's history.
•This work presents a high-resolution geochemical and paleontological record of the Oceanic Anoxic Event 2 in South America.•The La Luna Sea was in many regards biogeochemically similar to the modern Cariaco Basin.•Low amounts of organic carbon were buried in the epicontinental seas located on the western side of the Proto-Atlantic.•The La Luna Sea did not play an important role in carbon cycling during OAE2.
The Luna 20 mission returned samples from the Hilly and Furrowed Terrain of the Moon that is associated with the impact event that formed the Crisium Basin. This event potentially excavated deep ...crustal and upper mantle lithologies. Spinel is commonly considered to be a mineralogical indicator of rocks of high‐pressure origin, and orbital data indicate the presence of spinel‐bearing lithologies exterior to the basin. We have examined 166 Luna 20 particles in the 250–500 μm size range and found 31 spinel‐bearing fragments. Of these 10 are igneous plutonic Mg‐suite rocks, most of which are troctolitic, and 16 are impact melt rocks. The other five are fused soil or devitrified glass fragments. The spinel‐bearing lithic fragments are plagioclase‐rich and do not have the high modal abundances of Mg‐Al spinel previously identified in the region through remote sensing analyses. The textures, compositions, and inferred crystallization sequences of the present magmatic spinel‐bearing samples are most consistent with a relatively shallow crustal (rather than a deep crustal) origin, with a petrogenesis involving assimilation of ferroan anorthosite crust by Mg‐rich, mantle‐derived magmas. Both relict and newly formed spinels are found in impact melt rocks and are also inferred to have formed at relatively low pressures. Thus, the presence of spinel is not an unambiguous indicator of mantle or deep crustal material. The insights gained from this study show that studies of a small, robotically collected sample can improve our understanding of regional lithologies and petrologic processes.
Plain Language Summary
Lunar rocks that contain spinel have long been thought to have formed at high pressures and have deep sources. A survey of lithic fragments in the Luna 20 regolith shows that spinel occurs in igneous and impact melt rocks with features more consistent with relatively rapid cooling than with slow cooling, and therefore relatively shallow depths of origin. The presence of spinel in a lunar rock is not an unambiguous indicator of mantle or deep crustal material.
Key Points
Spinel‐bearing rock fragments found in the Luna 20 regolith provide insights into the origin and distribution of lunar spinel‐bearing lithologies
Evidence for rapid cooling suggests these lithologies did not have deep sources and probably formed at relatively shallow depths
A new mineral phase was discovered in the course of studies at the Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry (IGEM) of fine-grained fractions of the lunar ...regolith delivered to the Earth by the
Luna 16
,
Luna 20
, and
Luna 24
automatic stations. The grain of native niobium was identified in the regolith sample from the Mare Crisium. Presumably, this phase was formed during the fractioning process in a gas–plasma cloud under an impact event on the Moon.
Laser ionization mass spectrometry is one of the most promising methods for analysis of the elemental and isotopic composition of solids in space experiments: the required instruments are highly ...reliable and easy to operate, no sample preparation is needed, and the spatial resolution of this method is relatively high. In view of this, the LASMA-LR laser ionization mass spectrometer was included into the list of instruments for the future Luna-Glob (
Luna-25
) and Luna-Resurs-1 (
Luna-27
) missions, where it will be used to examine the elemental and isotopic composition of lunar regolith at the landing sites. The accuracy of LASMA-LR measurements depends to a considerable extent on the size of the statistical sample of the spectral dataset. This defines the temporal parameters of operation of the mass spectrometer in a space experiment. A series of spectra of enstatite (mineral found in lunar regolith) was measured, and the instrumental accuracy of measurements with spectral datasets of different sizes was estimated. It was demonstrated that an elemental analysis accuracy of 10% is achieved by processing a set of 300 spectra, which corresponds to ~4 h of continuous LASMA-LR operation. A measurement accuracy of 1% for isotopic distributions is achieved within the same 4-hour period only for isotopes with ratios no higher than 10 : 1, while the same accuracy for isotopes with higher ratios requires an unfeasibly long analysis time.
The paper's subject is fifteen copper alloy lamps of various types and sizes from the Roman Collection of the Archaeological Museum of Istria, mostly collected in the first half of the 20th century ...in Istria and on the island of Cres. The lamps were classified according to shape into six basic types and compared with other finds to gain insight into the chronological framework, workshop centers, and distribution routes. Figural depictions on lamps have been interpreted as mythological and cult significance. The available data on the circumstances of the findings were analyzed and compared with the other data, from which assumptions were made about the possible time and causes of the storage of copper alloy lamps in hoards. The possible value of the copper alloy lamps is estimated according to their weight.
We present two previously unreported hominin permanent teeth one right upper second molar (M2), one left lower second molar (m2) from Lunadong (“dong” = “cave”), Guangxi Zhuang Autonomous Region, ...China. The teeth are important because: 1) they were found in situ; 2) at least one (M2) can be confidently assigned to modern Homo sapiens, while the other (m2) is likely modern H. sapiens; and 3) the teeth can be securely dated between 126.9 ± 1.5 ka and 70.2 ± 1.4 ka, based on multiple MC-ICP-MS uranium-series dates of associated flowstones in clear stratigraphic context. The Lunadong modern H. sapiens teeth contribute to growing evidence (e.g., Callao Cave, Huanglongdong, Zhirendong) that modern and/or transitional humans were likely in eastern Asia between the crucial 120–50 ka time span, a period that some researchers have suggested no hominins were present in the region.
